The Beau Street Hoard: excavating Roman treasure, one coin at a time

Julia Tubman, conservator, British Museum

In November 2007, during a routine archaeological excavation in advance of building work in Beau Street, Bath (a stone’s throw from the famous Roman Baths themselves), archaeologists came upon what was clearly a very large number of coins contained within a cist (a stone-lined box). Upon further excavation, they quickly came to realise they were looking at one of the largest coin hoards found in the UK, representing quite a tumultuous time in Roman Britain – about AD 270.

When groups of coins that appear to be over 300 years old are found, they must be reported to the local coroner (according to the Treasure Act 1996). The coins enter what we call the ‘Treasure Process’ where, if necessary for identification, they will be cleaned in preparation for their formal declaration as Treasure and the property of the Crown, or eventual valuation. Usually this occurs at the British Museum, or in the case of Welsh Treasure cases, the National Museum of Wales.

In order to preserve its shape and context, the archaeologists cut around the hoard and lifted it in a soil block. As a metals conservator at the British Museum, my job is to excavate the coins from the soil and clean them up. The initial excavation should take about six weeks and during that time I will be regularly adding to this blog with updates of my work as it progresses. Colleagues from curatorial departments and our science team who are involved with the project will also contribute as the hoard gradually reveals its story.

The hoard in its soil block when it arrived in the conservation lab at the British Museum

The coins are currently held together by soil and metallic corrosion. They are blue and green in colour indicating the corrosion of a copper metal, which would have been used as a base alloy for the coins. Interestingly, within this copper corrosion is actually a layer of silver that was plated over the copper during the manufacture of the coins.

The coins have also maintained the shape of the cist they were contained within, as the soil and corrosion has concreted together. Looking more closely, we can even see that there are groups of coins within the hoard; which is because this large hoard appears to be composed of six individual smaller hoards.

We had an idea that this could be the case because in December last year Dr. Mavrogordato, from the Imaging Centre in the University of Southampton’s Department of Engineering Sciences, kindly took x-rays of the block. The resulting images show what look to be ‘bags’ of coins. We don’t know whether the bags themselves have survived (they could have been made of an organic material such as textile or leather), but the corroded coins have kept the shape of their containers and I will be looking for evidence of them.

The cleaning process is fine and detailed work

As my job will involve excavating the hoard, knowing that there are individual bags of coins gives me a very good starting point as it means I can deconstruct the soil block bag by bag. It will be very interesting to see if the coins were bagged together for a particular reason; for example, if they were grouped by emperor or denomination.

I’ve cleaned a few loose coins already and, after stripping away the copper corrosion, I’ve found some very impressive silver surfaces (nicer than we had previously hoped!) Given the large number of coins in the soil block, I’m hoping to be able to clean as many coins as possible using chemicals such as formic acid, rather than by hand using a scalpel. I have 18 months to complete this project, so time is of the essence.

The hoard in May 2012 in the conservation lab, excavation underway.

Initial estimates put the number of coins at around 30,000. After having excavated the block a little since then, guesses about the maximum number of coins in the hoard have decreased and estimates vary between everyone looking at it. Readers of the blog are welcome to suggest their own figures – I say no more than 22,000 coins, what do you think?

Removing the tough shell of the copper corrosion layer is important not just to find shiny surfaces but also to find the detail on the coins needed for identification by my colleagues in the Coins and Medals department, Eleanor Ghey and Richard Abdy (who will be blogging about the significance of the find next week). At this early stage in the project, I’m only cleaning the coins so that they can be identified: I’m not cleaning them for display, by completely removing all the corrosion or soil; that would require more time.

Some of the coins after being cleaned

When looking at Roman coins, specialists will be hoping to identify features on the ‘obverse’ (side bearing the bust of an emperor or an important relative) and the ‘reverse’ (side bearing representations of deities, animals, and other important Roman symbols). The subjects depicted on Roman coins varied according to emperor and coins of more than one emperor could be in circulation at any given time. On both sides, revealing enough of the ‘legend’ (the writing around the edge of the coin) is important, especially where the figure in the centre is very corroded or worn. Eleanor and Richard will also be looking closely for any mint marks on the coins (usually on the reverse) which indicate where in the empire the coin was struck, so I’ll have to be very careful when cleaning to reveal as much detail as possible.

Coins identified thus far have shown a real mix of the many Roman emperors of the third century AD (it was such a politically unstable time that many of them only got to reign a few years): Septimius Severus (AD 193-211), Gordian III (AD 238-249), Philip I (AD 244-249), Decius (AD 249-251), Trebonianus Gallus (AD 251-253), Aemilian (AD 253), Valerian I (AD 253-260), Gallienus (AD 253-268) and Postumus (AD 260- 268).

The Roman Baths Museum hopes to purchase the hoard and eventually display it to the public. It’s fantastic to know where the hoard might ultimately end up, and I’m working closely with curator Stephen Clews at the Roman Baths.

Reblogged this on Things of Historical Significance and commented:
As I made the highly intelligent decision of creating this blog during a period of epic procrastination from writing my essays, I’m now in a position where I’m too busy and frazzled to really do in-depth posts. So instead I thought I’d reblog this wonderful article from The British Museum Blog about the Beau Street Hoard of coins from Bath. Being a numismatist in the making, this has really excited me and I’m excited to see that Richard Abdy (head of Coins & Medals at BM) is involved with the project. I was lucky enough to attend a talk by Richard at The Barber Institute of Fine Arts (lucky as its part of my university) to coincide with their latest numismatics exhibit (Cityscapes: Panoramic Views on Coins and Medals) and he is a world-leading numismatist and truly interesting man and I may hopefully (fingers crossed) be working with him and the department for a few weeks this Summer, so I can question him persistently and annoyingly about the Hoard!

Well done!… I’m eager to view the coins next time I visit the Roman Baths Museum and the British Museum. I knew there’s much more attraction to Bath than the Georgian buildings and Jane Austen!… Thank you!

It really is amazing to think that the concept of a coin hasn’t changed in all of these years and that these coins are still in good enough shape that if you took them to a store, you could probably use them in a vending machine. That would be the most expensive candy bar ever

Fascinating story. I wonder if Julia Tubman could give us an idea of how she cleaned the coins. I notice tshe mentions formic acid – what concentration? When is this used in the process, is it her first step? I would dearly love the details of her treatment. (My wife has used for more than 30 years a BM recipe for cleaning antique furniture – it’s a cracker of a cleaner!!)